A conventional seat belt system is so constructed that a tongue plate attached to webbing is engaged with a corresponding buckle body paired with the tongue plate. This binds an occupant to a seat to absorb an impact at the time of a crash and the like, thereby protecting the occupant.
A plurality of seat belt systems are placed at a rear seat of a vehicle to bind more than two occupants to their respective seats. In order to prevent one occupant from mistakenly wearing a seat belt system for a neighboring occupant, a structure for preventing incorrect wearing has been adopted where appropriate (see patent publication 1, for example).
The structure of a seat belt system disclosed in patent publication 1 comprises a plurality of buckle units each being formed by a tongue plate and a buckle body into which the tongue plate is inserted. The buckle body has an ejector caused to move within the buckle body by the insertion of the tongue plate, and a hook member caused to pivot by being pushed by the movement of the ejector to thereby come into engagement with an engagement hole of the tongue plate.
The seat belt system of patent publication 1 comprises: a first buckle unit featuring a short distance from an insertion front end to an engagement hole of a tongue plate while allowing an ejector to move a long distance; and a second buckle unit featuring a long distance from an insertion front end to an engagement hole of a tongue plate while allowing an ejector to move a short distance.
When a tongue plate having a short distance from an insertion front end to an engagement hole is inserted into the second buckle unit allowing an ejector to move a short distance, the ejector moves a small amount. Thus a hook member is not pushed by the ejector and the hook member is not caused to pivot in a direction in which the hook member makes engagement with the engagement hole, thereby preventing inadvertent engagement.
When a tongue plate having a long distance from an insertion front end to an engagement hole is inserted into the first buckle unit allowing an ejector to move a long distance, the ejector reaches a position for pushing a hook member. Thus the hook member is pushed by the ejector and is then caused to pivot in a direction in which the hook member makes engagement. However, the engagement hole of the tongue plate has not reached a position for making engagement with the hook member, thereby preventing inadvertent engagement.
Patent Publication 1: Japanese Utility Model Publication No. 5-40728 (1993)
According to the conventional seat belt system described above, the engagement hole of the tongue plate has not reached a position for making engagement with the hook member when the tongue plate having a long distance from the insertion front end to the engagement hole is inserted into the first buckle unit allowing the ejector to move a long distance. This reliably prevents inadvertent engagement. However, the engagement hole of the tongue plate has reached a position for making engagement with the hook member when the tongue plate having a short distance from the insertion front end to the engagement hole is inserted into the second buckle unit allowing the ejector to move a short distance. This may disadvantageously cause the hook member to pivot in a direction in which the hook member makes engagement by the vibration, oscillation or the like of the buckle unit itself.